1. Field of the Invention
The present invention relates to a sound recording apparatus, and more particularly, to a recording apparatus for recording a standard sound signal for use in a video cassette recorder (VCR).
2. Description of the Prior Art
In video cassette recorders, a standard sound signal to be recorded onto a sound track is equalized before recorded. The equalizing is performed according to a recording speed mode such as EP (extended play) and SP (standard play) modes.
FIG. 1 shows a conventional circuit where equalizing is performed according to the EP or SP mode as described above. Numeral 1 is an operational amplifier. A sound signal is supplied to a plus input terminal thereof. To a minus input terminal thereof to which a negative feedback is applied through resistors R3 and R4, a first series circuit 2 is connected including an inductance coil L which is a discrete part, a capacitor C11 and a resistor R11 which circuit 2 is arranged between the minus input terminal and ground. To the minus input terminal, a second series circuit 3 is also connected including a capacitor C12, a resistor R12 and a switch 4 which circuit 3 is arranged between ground and a connection midpoint (a) located between the induction coil L and the capacitor C11. In the SP mode, the switch 4 is OFF. As a result, the capacitor C12 and the resistor R12 of the second series circuit 3 do not operate, and only the first series circuit 2 operates. Under this condition, the resonant frequency is, as shown by SP in FIG. 2, a comparatively high frequency f1 in middle and high bands. A gain of the amplifier 1 is boosted with the frequency f1 as the center.
In the EP mode, the switch 4 is ON. As a result, the second series circuit 3 operates in addition to the first series circuit 2. Under this condition, the resonant frequency is a low frequency f2 in the middle and high bands. A gain of the amplifier 1 is boosted with the frequency f2 as the center.
A sound signal is equalized in the above-described manner so that a predetermined band thereof is boosted in each recording speed mode. Thereafter, it is directed to a succeeding circuit (not shown), and is finally recorded onto a sound track of magnetic tape through a magnetic head.
In FIG. 2, the gain is not boosted in a band higher than the middle and high bands. This is because no sound signals are present in such a band of a standard sound signal for a video cassette recorder.
In the conventional circuit, since the discrete inductance coil L is used on the negative feedback side of the amplifier 1, the possibility is strong that noise is produced due to electromagnetic induction caused between the inductance coil L and a surrounding apparatus such as a television receiver.
Furthermore, since the cost of the discrete inductance coil is comparatively high compared to those of a capacitor and a resistor, the cost of the entire circuit increases. In addition, an additional work in manufacturing the VCR is required to connect the induction coil.